Catalytic metal substrates for purifying exhaust gas carry catalysts in order to purify problematic gas components, such as HC (hydrocarbons), CO (carbon monoxide) and NOx (nitrogen compounds), which impair the human body when emitted in the atmosphere.
A catalytic converter carrying a catalyst is used for purification of exhaust gas in automobiles and motorcycles, and is disposed in an exhaust gas path for the purpose of purification of exhaust gas in internal combustion engines. The metal substrate for catalytic converter is similarly used in a methanol reformer that steam reforms hydrocarbon compounds such as methanol to generate hydrogen-rich gas, a CO remover that reforms CO into CO2 to remove CO, and an H2 combustion apparatus that burns H2 into H2O to remove H2. Such a catalyst base material is formed by partially joining a honeycomb core and an outer jacket. The honeycomb core is formed by winding a flat metal foil and a corrugated metal foil, and the outer jacket surrounds the outer circumferential surface in the radial direction of the honeycomb core. The honeycomb core includes many exhaust gas channels extending in the axial direction. Exhaust gas can be purified by allowing exhaust gas to flow through this exhaust gas channel from the gas inlet side end surface toward the gas outlet side end surface of the honeycomb core.
Since the metal substrate for catalysts increases in temperature by receiving heat from exhaust gas, the honeycomb core suffers from heat distortion due to foil elongation. In addition, the temperature distribution in the axial direction of the base material for catalysts is not uniform, and the temperature is likely to be higher in the upstream portion than in the downstream portion of the exhaust gas channels. For this reason, heat distortion is larger on the upstream side of the exhaust gas channel. Accordingly, when the honeycomb core and the outer jacket are joined in the portion on this upstream side, a load applied to the joining section between the honeycomb core and the outer jacket increases during a thermal cycle of heating and cooling, possibly causing the honeycomb core to drop off from the outer jacket.
On the other hand, exhaust gas is required to be brought into contact with a wider area of the honeycomb core in order to increase purification performance of the honeycomb core. Furthermore, an increased pressure loss while exhaust gas flows through the honeycomb core leads to decrease in output of a vehicle.